create request context: keep parsed and string urls in sync
create request context: keep parsed and string urls in sync

ServerContext::GetQueryOptions modifies the url passed to it, removing any
ModPagespeedFoo=Bar query parameters.  CreateNewProxyFetch needs that modified
url but we were giving it the unmodified one.

Fixes #83

0x0mar/ngx_pagespeed,pagespeed/ngx_pagespeed,0x0mar/ngx_pagespeed,digideskio/ngx_pagespeed,digideskio/ngx_pagespeed,wanrui/ngx_pagespeed,wanrui/ngx_pagespeed,pagespeed/ngx_pagespeed